Memory is one type of integrated circuitry, and is used in computer systems for storing data. Such is typically fabricated in one or more arrays of individual memory cells. The memory cells might be volatile, semi-volatile, or non-volatile. Non-volatile memory cells can store data for extended periods of time, and in many instances including when the computer is turned off. Volatile memory dissipates and therefore requires to be refreshed/rewritten, and in many instances including multiple times per second. Regardless, the smallest unit in each array is termed as a memory cell and is configured to retain or store memory in an least two different selectable states. In a binary system, the storage conditions are considered as either a “0” or a “1”. Further, some individual memory cells can be configured to store more than two bits of information.
Integrated circuitry fabrication continues to strive to produce smaller and denser integrated circuits. Accordingly, the fewer components an individual circuit device has, the smaller the construction of the finished device can be. Likely the smallest and simplest memory cell will be comprised of two conductive electrodes having a programmable material received there-between. Example materials include metal oxides which may or may not be homogenous, and may or may not contain other materials therewith. Regardless, the collective material received between the two electrodes is selected or designed to be configured in a selected one of at least two different resistive states to enable storing of information by an individual memory cell. When configured in one extreme of the resistive states, the material may have a high resistance to electrical current. In contrast in the other extreme, when configured in another resistive state, the material may have a low resistance to electrical current. Existing and yet-to-be developed memory cells might also be configured to have one or more additional possible stable resistive states in between a highest and a lowest resistance state. Regardless, the resistive state in which the programmable material is configured may be changed using electrical signals. For example, if the material is in a high-resistance state, the material may be configured to be in a low resistance state by applying a voltage across the material.
The programmed resistive state is designed to be persistent in non-volatile memory. For example, once configured in a resistive state, the material stays in such resistive state even if neither a current nor a voltage is applied to the material. Further, the configuration of the material may be repeatedly changed from one resistance state to another for programming the memory cell into different of at least two resistive states. Upon such programming, the resistive state of the material can be determined by appropriate signals applied to one or both of the two electrodes between which the material is received.
Certain metal oxides can be used as such materials in resistive memory cells. During fabrication, the materials which make up the memory elements are deposited and patterned to produce a desired finish shape and construction of the individual memory cells in an array of such cells. Accordingly, a conductive material is deposited for one of the electrodes, followed by deposition of at least some metal oxide for the programmable region, and followed by deposition of more conductive material for the other electrode of the memory cell. Often, the first and second conductive layers are fabricated as elongated conductive lines which run generally parallel an outermost major surface of the substrate upon which such are fabricated, yet orthogonal relative to one another.
Regardless, the three different regions of the memory cell are often patterned by etching using multiple masking and etching steps. Such typically include anisotropic plasma etching through the conductive outer electrode material inwardly at least to the metal oxide which will be the programmable region of the memory cell. Further, usually subsequent plasma etching is conducted through the metal oxide to the lower electrode conductive material. Regardless, exposure of the metal oxide material to plasma etching can adversely affect the operation of the memory cell in that composition and/or structure of the metal oxide material may be modified in an unpredictable manner.